Process for the liquid phase synthesis of h-inp-(d)bal-(d)trp-phe-apc-nh2, and pharmaceutically acceptable salts thereof

Abstract

The present invention provides a process for the liquid phase synthesis of the Ghrelin analog H-Inp-(D)Bal-(D)Trp-Phe-Apc-NH2 (SEQ ID NO: 1, Formula (I)), pharmaceutically acceptable salts thereof.

What is claimed is: 
     
         1 . A process for the synthesis of a peptide of Formula (I)
   H-Inp-(D)Bal-(D)Trp-Phe-Apc-NH 2 ,   (I)
   or pharmaceutically acceptable salt thereof, comprising at least one step of coupling any two amino acids of the peptide of Formula (I) in a liquid phase.   
     
     
         2 . The process of  claim 1 , further comprising a step of reacting a silylating agent with a first amino acid selected form the amino acids of the peptide of Formula (I) in a polar aprotic organic solvent, thereby producing a first silylated amino acid. 
     
     
         3 . The process of  claim 2 , further comprising at least one step of coupling the first silylated amino acid with a second amino acid selected from the amino acids of the peptide of Formula (I). 
     
     
         4 . The process of any one of  claims 1  to  3 , comprising the step of reacting a silylating agent with the amino acid H-(D)Trp-OH in a polar aprotic organic solvent, thereby forming a silylated amino acid residue of the amino acid H-(D)Trp-OH or a salt thereof. 
     
     
         5 . The process of  claim 4 , further comprising the step of reacting the silylated amino acid residue of the amino acid H-(D)Trp-OH with an amino acid of the following formula
   X 1 -(D)Bal-Y 1 ,   thereby producing a peptide fragment of the following formula
   X 1 -(D)Bal-(D)Trp-OH, 
   or a salt thereof,   wherein X 1  is an amino protecting group, and Y 1  is a carboxyl activating group.   
     
     
         6 . The process of any one of  claims 1  to  3 , comprising the step of reacting a silylating agent with the amino acid H-Apc(X 2 )—OH in a polar aprotic organic solvent, thereby forming a silylated amino acid residue of the amino acid H-Apc(X 2 )—OH or a salt thereof, wherein X 2  is an amino protecting group. 
     
     
         7 . The process of  claim 6 , further comprising the step of reacting the silylated amino acid residue of the amino acid H-Apc(X 2 )—OH with an amino acid X 3 -Phe-Y 2 , thereby forming a peptide fragment of the following formula
   X 3 -Phe-Apc(X 2 )—OH
 
 
       or a salt thereof,
 wherein Y 2  is a carboxyl activating group, and X 3  is an amino protecting group. 
 
     
     
         8 . The process of  claim 7 , further including the step of reacting the peptide fragment of the following formula
   X 3 -Phe-Apc(X 2 )—OH,
   with an amidating agent, thereby producing a peptide fragment of the following formula
   X 3 -Phe-Apc(X 2 )—NH 2  or a salt thereof.
 
   
     
     
         9 . The process of  claim 8 , wherein the amidating agent is ammonia. 
     
     
         10 . The process of  claim 9 , further including the step of deprotecting the peptide fragment of the following formula
   X 3 -Phe-Apc(X 2 )—NH 2 ,
   thereby producing a peptide fragment of the following formula
   H-Phe-Apc(X 2 )—NH 2  
 
   
       or a salt thereof. 
     
     
         11 . The process of  claim 10 , further including the step of deprotecting the peptide fragment of the following structural formula
   X 1 -(D)Bal-(D)Trp-OH,   thereby producing a peptide fragment of the following formula
   H-(D)Bal-(D)Trp-OH 
   
       or a salt thereof. 
     
     
         12 . The process of  claim 11 , further comprising the step of reacting an amino acid X 4 -Inp-Y 3  with the peptide fragment of the following formula
   H-(D)Bal-(D)Trp-OH,   in a liquid solvent, thereby producing a peptide fragment of the following formula
   X 4 -Inp-(D)Bal-(D)Trp-OH 
   
       or a salt thereof,
 wherein X 4  is an amino protecting group, and Y 3  is a carboxyl activating group. 
 
     
     
         13 . The process of  claim 12 , wherein the liquid solvent is an organic solvent. 
     
     
         14 . The process of  claim 12 , further comprising the step of reacting the peptide fragment of the following formula
   X 4 -Inp-(D)Bal-(D)Trp-OH,   with the peptide fragment of the following formula
   H-Phe-Apc(X 2 )—NH 2 ,
 
   in the presence of a nucleophilic additive,   thereby producing a peptide fragment of the following formula
   X 4 -Inp-(D)Bal-(D)Trp-Phe-Apc(X 2 )—NH 2  
 
   
       or a salt thereof, 
       wherein X 2  is an amino protecting group. 
     
     
         15 . The process of  claim 14 , further including the step of deprotecting the peptide fragment of the following formula
   X 4 -Inp-(D)Bal-(D)Trp-Phe-Apc(X 2 )—NH 2 ,
   thereby producing the peptide fragment of Formula (I)
   H-Inp-(D)Bal-(D)Trp-Phe-Apc-NH 2    (I)
 
   
       or a salt thereof. 
     
     
         16 . The process of any one of  claims 1  to  3 , comprising the steps of:
 reacting a first silylating agent with the amino acid H-(D)Trp-OH in a first liquid solvent, thereby forming a silylated amino acid residue of the amino acid H-(D)Trp-OH or a salt thereof; 
 reacting the silylated amino acid residue of the amino acid H-(D)Trp-OH with an amino acid X 1 -(D)Bal-Y 1  in a second liquid solvent, thereby producing a peptide fragment of the following formula
   X 1 -(D)Bal-(D)Trp-OH 
 
 
       or a salt thereof, 
       wherein X 1  is an amino protecting group, and Y 1  is a carboxyl activating group;
 reacting a second silylating agent with the amino acid H-Apc(X 2 )—OH in a third liquid solvent, thereby forming a silylated amino acid residue of the amino acid H-Apc(X 2 )—OH, wherein X 2  is an amino protecting group; 
 reacting the silylated amino acid residue of the amino acid H-Apc(X 2 )—OH with an amino acid X 3 -Phe-Y 2  in a fourth liquid solvent, thereby producing a peptide fragment of the following formula
   X 3 -Phe-Apc(X 2 )—OH
 
 
 
       or a salt thereof, 
       wherein X 3  is an amino protecting group and Y 2  is a carboxyl activating group;
 reacting the peptide fragment of the following formula
   X 3 -Phe-Apc(X 2 )—OH,
 
 
 
       with an amidating agent in a fifth liquid solvent, thereby producing a peptide fragment of the following formula
   X 3 -Phe-Apc(X 2 )—NH 2  
 
 
       or a salt thereof;
 deprotecting the peptide fragment of the following formula
   X 3 -Phe-Apc(X 2 )—NH 2 ,
 
 
 
       thereby producing a peptide fragment of the following formula
   H-Phe-Apc(X 2 )—NH 2  
 
 
       or a salt thereof;
 deprotecting the peptide fragment of the following formula
   X 1 -(D)Bal-(D)Trp-OH, 
 
 
       thereby producing the peptide fragment of the following formula
   H-(D)Bal-(D)Trp-OH 
 
       or a salt thereof;
 reacting an amino acid X 4 -Inp-Y 3  with the peptide fragment of the following structural formula
   H-(D)Bal-(D)Trp-OH, 
 
 
       in a sixth liquid solvent, thereby producing a peptide fragment of the following formula
   X 4 -Inp-(D)Bal-(D)Trp-OH 
 
       or a salt thereof, 
       wherein X 4  is an amino protecting group, and Y 3  is a carboxyl activating group;
 reacting the peptide fragment of the following formula
   X 3 -Inp-(D)Bal-(D)Trp-OH 
 
 
       with the peptide fragment of the following structural formula
   H-Phe-Apc(X 2 )—NH 2 ,
 
 
       in the presence of a nucleophilic additive, in a seventh liquid solvent, thereby producing a peptide fragment of the following formula
   X 4 -Inp-(D)Bal-(D)Trp-Phe-Apc(X 2 )—NH 2  
 
 
       or a salt thereof; and
 deprotecting the peptide fragment of the following structural formula
   X 4 -Inp-(D)Bal-(D)Trp-Phe-Apc (X 2 )—NH 2 ,
 
 
 
       thereby producing the peptide fragment of Formula (I)
   H-Inp-(D)Bal-(D)Trp-Phe-Apc-NH 2    (I)
 
 
       or a salt thereof. 
     
     
         17 . The process of  claim 16 , wherein the first through the seventh liquid solvent, each independently, is an organic solvent. 
     
     
         18 . The process of  claim 2 ,  4 , or  6 , wherein the silylating agent is (trimethylsilyl)-N-dimethyl-acetamide. 
     
     
         19 . The process of  claim 16 , wherein the first and the second silylating agents, each, is (trimethylsilyl)-N-dimethyl-acetamide. 
     
     
         20 . The process of  claim 14  or  16 , wherein the nucleophilic additive is selected from the group consisting of 2-hydroxypyridine-N-oxide (HOPO), 1-hydroxy-7-azabenzotriazole (HOAt), 1-hydroxy-benzotriazole (HOBt), 3,4-dihydro-3-hydryoxy-4-oxo-1,2,3-benzotriazine (HODhbt), and ethyl-1-hydroxy-1H-1,2,3-triazole-4-carboxylate (HOCt). 
     
     
         21 . The process of  claim 20  wherein the nucleophilic additive is 2-hydroxypyridine-N-oxide (HOPO). 
     
     
         22 . The process of any one of  claim 5 ,  7 ,  12 , or  16  wherein the carboxyl activating groups Y 1 , Y 2 , and Y 3 , each independently, are selected from the group consisting of N-hydroxysuccinimide (HOSu), N-hydroxyphthalimide, pentafluorophenol (PfpOH), and di-(p-chlorotetrafluorophenyl)carbonate. 
     
     
         23 . A peptide fragment of structural formula (II)
   Boc-Inp-(D)Bal-(D)Trp-Phe-Apc(Boc)-NH 2 ,   (II)
   or a salt thereof.   
     
     
         24 . A peptide fragment of structural formula (III)
   Boc-Inp-DBal-DTrp-OH,   (III)
   or a salt thereof.   
     
     
         25 . A peptide fragment of structural formula (IV)
   H-Phe-Apc(Boc)-NH 2 ,   (IV)
   or a salt thereof.   
     
     
         26 . A peptide fragment of structural formula (V)
   H-DBal-DTrp-OH,   (V)
   or a salt thereof.   
     
     
         27 . A peptide fragment of structural formula (VI)
   Z-Phe-Apc(Boc)-NH 2 ,   (VI)
   or a salt thereof.